Theropods are clappers, not slappers

One of the most pervasive but subtle errors of the Jurassic Park series LINK is the idea that theropod hands kind of fold forwards and down as if they are about to slap their thighs in some entertaining dinosaurian Bavarian dancing routine. In fact the palms of the hands should face inwards as if about to give a nice round of applause. Theropods were clappers, not slappers.

This is pretty pervasive in the minds of the pubic from the iconic moment of terror-inducement to children as a Velociraptor opens a door. It’s interesting to note that people seem to have accepted this position of the manus as more or less de-facto correct without even thinking about it. I have recently done a bit of work on a dinosaur book for kids and I think every single theropod that was sent to me had slappy hands. Every single one I sent back and told them to reorientate them, because they were wrong and that they didn’t look like that in pretty much any theropod and then a week later the next one would come in and well, you can guess where the hands were.

We actually have good evidence from two very different sources that theropods could not put their hands in this position (well a few derived ones may have been able to approach it). Most obviously when we have good 3-D skeletons we can simply articulate the bones to see A) what their natural position was, and B) how well they could pronate the arm (that is rotate the lower arm at the elbow towards a slapping position, something humans are exceptionally good at). Secondly we can see that even when actually wanting to do something like support the weight of themselves which you might think you’d really want to use the flat of your hand, rather than just the edge a theropod still does not (or more likely therefore cannot) pronate the hand. This comes from a recently reported fossilised print of a resting theropod with nice prints for the edges of the hand.

I should add that as ever this is biology and well probably they could we really can’t be sure exactly how they folded their arms. Doubtless some were better at this than others and could be proper slappers if you like and of course even those which you might call a ‘true’ clapper, could still pronate a bit, but as a general rule of thumb this is portrayal is accurate.

So the next time you see a slap-handed theropod remember to clap. Hmmm, that sounds awfully like the last ‘advice to kids’ line from the end of an 80’s cartoon. I think I’d probably better stop about there.

PS Thanks to Jerry Harris, Andrew Milner and Corwin Sullivan for discussions on this one, a bit out of my normal range.

There is of course some variation in how well theropods can turn the wrist and lower arm, but essentially (to my knowledge) nothing can turn the arms so that they face the ground directly (i.e. the palms are parallel with the ground). SOme of the derived maniraptorans might get close (dromaeosaurs, troodontids and oviraptorosaurs). Most of the others would be luck to get halfway there and the normal position would most likely be a clapping one. I’m sure there were exceptions 9we are talking about hundreds of species here, few of which have been looked at in great detail etc.) but as a rule of thumb they really are clappers.

Quite interesting, I had (still have) the intention of reading more about this specific detail (by curiosity alone but also to draw accurate illustrations), but my hunch and overall impression regarding possible frequent mistakes in dinosaurian illustrations was much in the opposite direction.

While older illustrations used to depict dinosaurs with “flapping” hands, I’ve noticed that more recent ones, perhaps increasingly more commonly after the Chinese fossil “boom” of the late 90s, they were frequently drawn with “clapping” hands, which I thought to be motivated by the increase in popular knowledge (at least to the extent it can be said to be popular) of the link between dinosaurs and birds, and the consequent more bird-like depictions of theropod dinosaurs. Perhaps even a mistaken intuition, when using birds as a reference, assuming/guessing/betting on a trait to be ancestral when it might be more bird-specific (it’s not uncommon to see that, like pterosaurs with yellow beaks (which I think is actually worse), even though they actually nailed regarding the feathers in some dinos). Actually, I think I recall reading G. S. Paul pointing something related with the hand positioning as an argument in favor of his “dromaeosaurs as secondary flightless birds” theory; if I’m not misremembering it, and I might well be, the clapping hand would be a bird-specific adaptation to flight, retained in related flightless birds thought to be “just” dinos.

Whatever were the explanation, secondary flightless dinos or just some exaptation, I was almost “sure” that what I would find when I looked about more deeply was that the “slapping” position was primitive (after all, they came from quadrupeds at some point), guessing that it wouldn’t be much unusual in theropods, and that the “clapping” position would be more specific to the ones closer to birds/potentially flightless birds. I just wanted to look about how exactly paleontologists know that, and when in the phylogenetic tree the change happened. How surprising to find that the reality may be almost as close to the complete opposite as it could be.

I can pronate my hands quite well. There are times I have HAD to be on all fours, resting my hands on the ground. I as often held them in clapping position as in slapping position. In other words, I want to see the skeletal proofs before I say they could not pronate their hands.

It’s not that I want to draw them slapping, since I’ve way most often drawn them with palms facing in–better to GRAB with!!!!–but broad claims like this are better served by proof, rather than some photos of a few tracks.

But there is work on this that has been published to show how the bones would (or rather could / could not) move into various positions. Theropods are not humans and their bones are different which allows for a different and more limited) range of motion. The tracks are merely a further line of evidence. Try:
Carpenter KGudo M; Gutmann M; Scholz J (2002) Forelimb biomechanics of nonavian theropod dinosaurs in predation. Concepts of Functional, Engineering and Constructional Morphology. Senckenbergiana Lethaea 82: 59–76

this will be a bit embarrassing, but I always picture those slappy hands of theropods to grab an old lady’s handbag. You know, the kind of little old lady from the comic books who wears a long raincoat, a bun, huge black-rimmed glasses, and used both hands to grab a large black leather handbag from above? And in the next pane slaps it around the bank robber’s ears?

That’s what the slappy hands look like to me.

Incidentally, the ancestral condition is the clapping one, and it is preserved in many animals. Why do sauropod go to so much trouble of shifting the radius fully to the front of the ulna (Matt Bonnan’s papers comes to mind)? And then there is Plateosaurus, wholly incapable of pronation to any significant degree. And the Otozoum track with the supinated hands….. Plenty of evidence.

Bonnan, M.F. 2003. The evolution of manus shape in sauropod dinosaurs: implications for functional morphology, forelimb orientation, and sauropod phylogeny. Journal of Vertebrate Paleontology, 23(3): 595-613.
Bonnan, M.F. and A.M. Yates. 2007. A new description of the forelimb of the basal sauropodomorph Melanorosaurus: implications for the evolution of pronation, manus shape and quadrupedalism in sauropod dinosaurs; pp. 157-168 in Barrett, P. M. and D.J. Batten (eds.), Evolution and palaeobiology of early sauropodomorph dinosaurs. Special Papers in Palaeontology, 77.
Bonnan, M.F. and P. Senter. 2007. Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?; pp. 139-155 in Barrett, P. M. and D.J. Batten (eds.), Evolution and palaeobiology of early sauropodomorph dinosaurs. Special Papers in Palaeontology, 77.

Otozoum:
E. C. Rainforth. 2003. Revision and re-evaluation of the Early Jurassic dinosaurian ichnogenus Otozoum. Palaeontology 46(4):803-838
(hope that is the right one, I am not able to access my PDF collection right now).